1. Field of the Invention
The present invention relates to a dental implant and in particular to a dental implant with a shock absorbent cushioned interface between the implant and the embedding alveolar process, and a more physiological gingival attachment.
2. Description of the Related Art
Normally a living tooth has a root which rests in the periodontal membrane between the root of the tooth and the jaw. This membrane consists of millions of tiny fibers that together provide a cushion which spreads and distributes the impact force transmitted from the tooth to the jaw during mastication. In other words it acts as a shock absorber and has a damping effect on the impact force which the tooth receives thus providing a degree of flexibility between the tooth and the alveolar process of the jaw. The gingival tissue connects to the top of the root, sealing it from the oral fluids and pathogens.
Conventional dental implants rely on direct adhesion of bone tissue to the implant Without the intervening periodontal membrane. Without the cushioning effect of the periodontal membrane the impact stress concentrations which the jaw bone encounters from an implant often result over time in bone resorption and loosening of the implant or trauma to the overlying soft tissue.
The dental community over the past forty years has attempted to develop endosseous and subperiosteal dental implants which could be considered successful and effective. The 1978 NIH-Harvard Consensus Development Conference recommended that only those implants which provide functional service for five years in 75 percent of the cases be considered successful (Schnitman, P. A. and Schulman, L. B. eds; Dental Implants Benefit and Risks; Department of Health and Human Resources, 1980, p. 329). The American Dental Association indicates that as many as 60 percent of the currently used endosseous and unilateral subperiosteal implants have failed after only two years or less (American Dental Association, Dentist's Desk Reference: Materials, Instruments and Equipment, 1981, p. 149).
Endosseous implants lie in the jaw bone. The portion of these implants which is positioned beneath the gum tissue (gingival tissue) in the jaw bone is the root portion. The upper portion of the endosseous implant extends through the gum tissue into the mouth to support artificial teeth and other dental devices. Endosseous implants are made of metallic, ceramic, or polymeric materials.
Dental implants are typically made of mechanically suitable and biocompatible materials. Biocompatible materials do not corrode in the oral environment or adversely affect either the soft or bony tissue of the mouth. Mechanically suitable materials withstand the normal forces of chewing without bending, fracturing, or otherwise becoming mechanically compromised. Suitable materials which have been previously developed include: metals, such as cobalt chromium alloys, stainless steels, and titanium or titanium alloys; ceramic, such as aluminum oxide or hydroxylapatite; and several polymers and carbon compositions.
As time progressed, implantation techniques and endosseous implant designs have been refined. Early trials revealed that implants had to be inserted firmly in sufficient volumes of mandibular or maxillary bone. Implants placed loosely in a bone socket became surrounded by fibrous tissue and through progressive movement failed. Thick or large diameter implants placed in thin, bony ridges were not supported by sufficient volumes of bone implants with sharp edges or undercuts in the root portion produced stress concentrations which destroyed surrounding bone (bone resorption). Accordingly, endosseous dental implants must be in tight fitting bony sockets and have small diameter or thin wedge-shaped designs for suitable stress distribution. Given these design and implant considerations, bone is most likely to closely appose and support (ankylose) the root structure of an implant.
More recently, problems at the gingival tissue/implant interface have been addressed. In the human, natural teeth and gingival tissue form a seal where the teeth pass through the gingival tissue. This area of sealing is known as the pergingival site. At the pergingival site, gingival connective tissue, and in particular gingival epithelium (the protective layer of cells on the surface of the gingiva), join with the surface layer of the tooth, thus isolating the underlying soft and bony tissues from the oral environment. Early prosthetic dental implants did not seal where they passed through the gingival tissue and consequently left underlying tissues susceptible to foreign materials, including bacteria.
U.S. Pat. No. 4,531,916, issued to T. V. Scantlebury et al, discloses a dental implant providing an improved seal at the pergingival site, i.e. the area where the teeth pass through the gingival tissue. This dental implant device includes a root structure, a cervical segment which is connected to and projects above the root structure, and a gingival interface. The non-physiological gingival interface is formed of expanded polytetrafluoroethylene having a porous microstructure for the ingrowth of connective tissue. The root structure may be porous or non-porous. Where porous, there is an ingrowth of bony tissue into the root structure, where non-porous, the bone should grow so that the root structure becomes ankylosed in the jaw bone. Ingrowth of bony tissue into the root structure or ankylosis results in a structure which has poor energy absorption properties and the interface becomes increasingly rigid over time. Mechanical forces generated during mastication result in increased stress and wear on the dental implant and increased discomfort to the user.
The dental implant according to present invention provides an improved more physiological gingival interface which prevents bacterial penetration while retaining resiliency where the implant extends into the oral cavity. In addition, the invention provides the missing cushion effect naturally provided by the periodontal membrane.